#include <iostream>

using namespace std;

#include <lemon/utility.h>

using namespace std;

/*

struct _EmptyList {

  void write() const {}

};

template <typename _Item, typename _Next>

struct _AddNode {

  typedef _Next Next;

  typedef _Item Item;

  const Item item;

  const Next& next;

  _AddNode(const Item& _item, const Next& _next) 

    : item(_item), next(_next) {}

  void write() const {

    next.write();

    cout << item << ' ';

  }

};

template <typename _List = _EmptyList>

struct _Writer {

  typedef _List List;

  const List list;

  _Writer(const List& _list = List()) : list(_list) {}

  template <typename Item> _Writer<_AddNode<Item, List> > add(Item item) const {

    return _Writer<_AddNode<Item, List> >(_AddNode<Item, List>(item, list));

  }

  void write() const {

    list.write();

    cout << endl;

  }

};

typedef _Writer<> Writer;

int main() {

  Writer().add(3).add("alpha").add(4.53).write();

}

*/

class A {

public:

  typedef int X;

};

class C {

};

template <typename A> 

class TRUE {

public:

  static const bool state = true;

};

template <typename _A> 

class B {

public:

  typedef enable_if<A::X, int> state;

};

template <typename _A>

class B<_A, void> {

public:

  static const bool state = true;

};

int main() {

  printf("%s\n", B<A>::state(), true ? "true" : "false");

  printf("%s\n", B<C>::state(), true ? "true" : "false");

  return 0;

}